Time of flight (TOF) sensor with transmit optic providing for reduced parallax effect

ABSTRACT

A transmit integrated circuit includes a light source configured to generate a beam of light. A receive integrated circuit includes a first photosensor. A transmit optic is mounted over the transmit and receive integrated circuits. The transmit optic is formed by a prismatic light guide and is configured to receive the beam of light. An annular body region of the transmit optic surrounds a central opening which is aligned with the first photosensor. The annular body region includes a first reflective surface defining the central opening and further includes a ring-shaped light output surface surrounding the central opening. Light is output from the ring-shaped light output surface in response to light which propagates within the prismatic light guide in response to the received beam of light and which reflects off the first reflective surface.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of United States application for patentSer. No. 16/401,209, filed May 2, 2019, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

The present invention generally relates to a time of flight (TOF) sensorand, in particular, to a transmit optic for use in a TOF sensor.

BACKGROUND

A time of flight (TOF) sensor is well known to those skilled in the art.FIG. 1 presents a cross-sectional view of a typical prior art TOF sensor10. The sensor includes a support substrate 12 which may includeinterconnection wiring 14, 16, 18 that is embedded within the substrate12 and further located on the front surface 20 and rear surface 22 ofthe substrate. The wiring 16 within the substrate serves to interconnectthe wiring 14 on the front surface 20 to the wiring 18 on the rearsurface 22. A transmitter integrated circuit chip 30 is mounted to thefront surface 20 of the substrate 12 and electrically connected to thewiring 14 (using bonding wires or other electrical connection means wellknown to those skilled in the art). The transmitter integrated circuitchip 30 includes a light source 32 (for example, a vertical-cavitysurface-emitting laser (VCSEL)). A receiver integrated circuit chip 34is also mounted to the front surface 20 of the substrate 12 andelectrically connected to the wiring 14 (using bonding wires or otherelectrical connection means well known to those skilled in the art). Thereceiver integrated circuit chip 34 includes a first photosensor 36 anda second photosensor 38. The photosensors 36, 38 may, for example, eachcomprise an array of single-photon avalanche diodes (SPADs). The firstphotosensor 36 functions as a reference signal detector and the secondphotosensor 38 functions as an object signal detector. The integratedcircuit chips 30 and 34 are enclosed in an opaque housing 40 that ismounted to the front surface 20 of the substrate 12. The housing 40includes a transmit optic 42 (for example, a transparent glass plate)aligned with the light source 32 and a receive optic 44 (for example, atransparent glass plate) aligned with the second photosensor 38. Acentral partition 46 of the housing 40 is positioned between the firstphotosensor 36 and the second photosensor 38 to function as a lightisolation barrier.

Operation of the TOF sensor 10 involves triggering the emission of apulse of light by the light source 32. A first portion 50 of the emittedlight passes through the transmit optic 42 and is directed toward anobject 52. A second portion 54 of the emitted light is reflected by aninner surface of the housing 40 and is detected by the first photosensor36. The first portion 50 of the emitted light reflects from the object52, and the reflected light 56 passes through the receive optic 44 andis detected by the second photosensor 38. The difference in time betweenthe detection of the second portion 54 by the first photosensor 36 andthe detection of the reflected light 56 by the second photosensor 38 isindicative of the distance d between the TOF sensor 10 and the object52.

TOF sensors having the configuration as generally shown in FIG. 1 sufferfrom a number of problems as illustrated by FIG. 2 . The TOF sensorpossesses a transmit field of view 60 for the light source 32 and thetransmit optic 42 and a receive field of view 62 for the secondphotosensor 38 and the receive optic 44. One problem relates toparallax. Parallax is introduced by the separation distance s betweenthe transmit optic 42 and the receive optic 44. As a result, there is aspace 64 between the fields of view 60 and 62 where objects 52 cannot beseen and detected. Furthermore, problems with ranging spikes can beexperienced with respect to region 66 just further than the nearestdetectable distance d′. Also, the extreme edge areas 68 of the transmitfield of view 60 are susceptible to concerns with poor mode mixing of amulti-modal VCSEL output light pulse.

There is a need in the art to address the forgoing problems.

SUMMARY

In an embodiment, a time of flight (TOF) sensor comprises: a transmitintegrated circuit including a light source configured to generate acollimated beam of light; a receive integrated circuit including a firstphotosensor; and a transmit optic mounted over the transmit integratedcircuit and the receive integrated circuit, said transmit optic formedby a prismatic light guide configured to receive the beam of light andhaving an annular body region surrounding a central opening which isaligned with the first photosensor, the annular body region including afirst reflective surface defining the central opening and furtherincluding a ring-shaped light output surface surrounding the centralopening and configured to output light in response to light thatpropagates within the prismatic light guide in response to the receivedbeam of light and which reflects off the first reflective surface.

In an embodiment, a prismatic light guide receives a beam of light andincludes an annular body region surrounding a central opening. Theannular body region of the prismatic light guide includes a firstreflective surface defining the central opening and further includes aring-shaped light output surface surrounding the central opening andconfigured to output light in response to light that propagates withinthe prismatic light guide in response to the received beam of light andwhich reflects off the first reflective surface.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the embodiments, reference will now bemade by way of example only to the accompanying figures in which:

FIG. 1 is a cross-sectional view of a typical prior art TOF sensor;

FIG. 2 illustrates parallax concerns with the sensor of FIG. 1 ;

FIGS. 3A-3B show isometric and partially transparent views of a transmitoptic;

FIG. 3C is a cross-section of a microlens structure;

FIGS. 4A-4B are top and bottom perspective views of the transmit optic;

FIGS. 4C-4D are cross-sectional views of the transmit optic;

FIG. 4E is a side view of the transmit optic;

FIG. 5 is a cross-sectional view of a TOF sensor incorporating thetransmit optic.

DETAILED DESCRIPTION

Reference is now made to FIG. 3A which shows an isometric and partiallytransparent view of a transmit optic 100 for use in a time of flight(TOF) sensor. FIG. 3B shows a cross-section of the isometric andpartially transparent view of FIG. 3A. The transmit optic 100 is aprismatic light guide formed by a unitary body of highly opticallytransparent material such as polycarbonate or poly methyl methylacrylate(PMMA). The unitary body of the transmit optic 100 is preferably madeusing an injection molding process followed by optical finishing ofexternal surfaces in a manner well known to those skilled in the art.Furthermore, certain external surfaces of the molded unitary body whichare desired to be reflective may be treated with a mirror coating inmanner well known to those skilled in the art.

The unitary body of the transmit optic 100 includes an annular bodyregion 102 and a radial projection region 104. The annular body region102 is in the form of a ring which encircles a central opening 106 andhas a radial cross-section in the general shape of a trapezoid where thelonger side of the two parallel sides of the trapezoidal cross-sectiondefines a light outlet surface 110 of the transmit optic 100. The lightoutlet surface 110 is ring-shaped (in a plane perpendicular to an axisof the central opening and is preferably textured and/or patterned toinclude a plurality of microlens 158 structures (for example, convex incross-section as shown in FIG. 3C), wherein each microlens 158 may havea size and shape as needed in order to produce a desired beam divergence(reference 160). With this annual body region configuration, the centralopening 106 takes the shape of a truncated cone (i.e., it isfrusto-conical in shape). The outer and inner non-parallel sides of thetrapezoidal cross-section respectively define angled light reflectingsurfaces 112 and 114 (more specifically, internally light reflectingsurfaces) which may, for example, have a mirror coating for reflectionor be configured as total internal reflection surfaces. The shorter sideof the two parallel sides of the trapezoidal cross-section defines partof a base surface 116 of the transmit optic 100, and as will bedescribed in more detail herein a portion of this base surface providesthe light input surface of the transmit optic 100. The base surface 116may further be treated to be reflective (for example, by use of a mirrorcoating layer).

The radial projection region 104 extends in a radial direction out fromthe annular body region 102. The radial projection region 104 may have across-section perpendicular to the radial direction in the general shapeof a rectangle or square. A first pair of opposed parallel sides 120 ofthe rectangular or square cross-section are extensions of the outernon-parallel side of the trapezoidal cross-section for the annular bodyregion 102 associated with the reflecting surface 112. A second pair ofopposed parallel sides 122 of the rectangular or square cross-sectionare extensions of the light outlet surface 110 and base surface 116. Thedistal end of the radial projection region 104 includes an angled lightreflecting surface 128 (more specifically, an internally lightreflecting surface) which may, for example, have a mirror coating forreflection or be configured as a total internal reflection surface. Theportion of the base surface 116 associated with the parallel side 122 inthe radial projection region 104 is shaped to include a collimatingoptical lens 132 whose optical axis is aligned to intersect at theangled light reflecting surface 128.

The collimating optical lens 132 receives divergent light 150 emittedfrom an external light source (not shown) and collimates the receivedexternal light to produce a beam 152 directed towards the angled lightreflecting surface 128. The beam 152 is reflected by the angled lightreflecting surface 128 to produce a beam 154 which propagates throughthe radial projection region 104 generally in a radial direction towardsthe central opening 106. The beam 154 is reflected by the reflectingsurface 114 to produce a beam 156 directed towards the light outletsurface 110 and the plurality of microlens 158 structures. The microlens158 structures refract the beam 156 to produce a spread of beams 160. Itwill be understood, even though not explicitly illustrated in FIG. 3B,that portions of the beam 154 will in effect spread when propagatingthrough the radial projection region 104 and could bounce of othersurfaces of the prismatic light guide before reaching the microlens 158structures. The illustrated paths for beams 154, 156 and 160 is just oneexample of light propagation within the prismatic light guide of thetransmit optic 100. Illumination from the received collimated light 150will be output across the light outlet surface 110 at locations whichsurround the central opening 106.

FIGS. 4A-4B are top and bottom perspective views of the transmit optic100, FIGS. 4C-4D are cross-sectional views of the transmit optic 100taken along lines 4C and 4D, respectively, of FIG. 4A, and FIG. 4E is aside view of the transmit optic 100.

Reference is now made to FIG. 5 which presents a cross-sectional view ofa TOF sensor 200 that utilizes the transmit optic 100. The sensorincludes a support substrate 212 which may include interconnectionwiring 214, 216, 218 that is embedded within the substrate 212 andfurther located on the front surface 220 and rear surface 222 of thesubstrate. The wiring 216 within the substrate serves to interconnectthe wiring 214 on the front surface 220 to the wiring 218 on the rearsurface 222. A transmitter integrated circuit chip 230 is mounted to thefront surface 220 of the substrate 212 and electrically connected to thewiring 214 (using bonding wires or other electrical connection meanswell known to those skilled in the art). The transmitter integratedcircuit chip 230 includes a light source 232 (for example, avertical-cavity surface-emitting laser (VCSEL)). A receiver integratedcircuit chip 234 is also mounted to the front surface 220 of thesubstrate 212 and electrically connected to the wiring 214 (usingbonding wires or other electrical connection means well known to thoseskilled in the art). The receiver integrated circuit chip 234 includes afirst photosensor 236 and a second photosensor 238. The photosensors236, 238 may, for example, each comprise an array of single-photonavalanche diodes (SPADs). The first photosensor 236 functions as areference signal detector and the second photosensor 238 functions as anobject signal detector. The integrated circuit chips 230 and 234 areenclosed in an opaque housing 240 that is mounted to the front surface220 of the substrate 212. The housing 240 supports the transmit optic100 with the collimating lens 132 aligned with the light source 232 andthe central opening 106 aligned with the second photosensor 238. Anadhesive may be used to mount the transmit optic 100 to the housing 240.A central partition 246 of the housing 240 is positioned between thefirst photosensor 236 and the second photosensor 238 to function as alight isolation barrier.

A light pipe 260 with a receive optic 262 (for example, a transparentplate) is mounted within the central opening 106. The light pipe has theshape of a truncated cone (i.e., frusto-conical) with a central borewithin which the receive optic 262 is installed. The outer conicalsurface of the light pipe 260 may be adhesively bonded to the innerconical surface 114 transmit optic 100. The light pipe may be made of anoptically opaque molded material.

Operation of the TOF sensor 200 involves triggering the emission of apulse of light by the light source 232. A first portion 250 of theemitted light forms the divergent light 150 which is directed towardsthe collimating lens 132 and passes through the transmit optic 100 to beemitted from the light outlet surface 110 as the spread of beams 160which are directed toward an object 252. A second portion 254 of theemitted light is reflected by the base surface 116 of the transmit optic100 and is detected by the first photosensor 236. The first portion 250of the emitted light reflects from the object 252, and the reflectedlight 256 passes through the light pipe 260 and receive optic 262 and isdetected by the second photosensor 238. The difference in time betweenthe detection of the second portion 254 by the first photosensor 236 andthe detection of the reflected light 256 by the second photosensor 238is indicative of the distance d between the TOF sensor 200 and theobject 252.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims.

What is claimed is:
 1. A system, comprising: a first optic, comprising:an annular body region surrounding a central opening defined by a firstreflective surface; wherein said annular body region includes aring-shaped light output surface surrounding the central opening;wherein the first reflective surface defining the central opening isconical in shape; a radial projection region extending in a radialdirection away from the annular body region; wherein said radialprojection region includes a lower surface and a second reflectivesurface extending between an extension of the ring-shaped light outputsurface and the lower surface; and a collimating lens located on thelower surface of said radial projection region and having an opticalaxis aligned to intersect with said second reflective surface; and asecond optic comprising: a light pipe having a bore; wherein an outersurface of the light pipe is conical in shape; and wherein the lightpipe is mounted within the central opening of the annular body region.2. The system of claim 1, wherein said collimating lens is configured toreceive a beam of light and produce a collimated beam of light that isreflected by said first and second reflective surfaces to produce anoutput beam of light at said ring-shaped light output surface.
 3. Thesystem of claim 1, further comprising a plurality of microlenses locatedon the light output surface.
 4. The system of claim 3, wherein eachmicrolens has a convex shape.
 5. The system of claim 1, furtherincluding an adhesive material for securing the conical outer surface ofthe light pipe to the conical first reflective surface of the annularbody region.
 6. The system of claim 1, further comprising: a lightsource configured to generate a beam of light directed towards saidcollimating lens; and a light sensor configured to receive light passingthrough the bore of the light pipe.
 7. The system of claim 1, whereinthe conical first reflective surface has a mirror coating.
 8. The systemof claim 1, further comprising a light source configured to generate abeam of light directed towards said collimating lens.
 9. A system,comprising: a first optic formed by a prismatic light guide, whereinsaid prismatic light guide comprises: an annular body region surroundinga central opening; a radial projection region extending in a radialdirection away from the annular body region, wherein a surface of theradial projection region includes a collimating lens configured toreceive a beam of light and produce a collimated beam of light; theannular body region including a first reflective surface defining thecentral opening and configured to internally reflect the collimated beamof light; and a light output surface surrounding the central opening ina ring-shape and configured to output light in response to theinternally reflected collimated beam of light; and a second opticcomprising: a light pipe having a bore; wherein the light pipe ismounted within the central opening of the annular body region.
 10. Thesystem of claim 9, wherein the radial projection region further includesa second reflecting surface configured to internally reflect thecollimated beam of light through the radial projection region andtowards the first reflecting surface.
 11. The system of claim 10,wherein an optical axis of the collimating lens is aligned to intersectwith the second reflecting surface.
 12. The system of claim 10, whereinthe beam of light is divergent and where the collimating lens isconfigured to collimate the divergent beam of light to provide thecollimated beam of light.
 13. The system of claim 10, wherein thecollimated beam of light propagates, after being internally reflected bythe second reflecting surface, through the prismatic light guide in adirection parallel to said radial direction and is reflected by thefirst reflective surface towards the light output surface.
 14. Thesystem of claim 13, wherein the first reflective surface is a conicalsurface.
 15. The system of claim 9, wherein the light output surfaceincludes a plurality of microlenses.
 16. The system of claim 15, whereineach microlens has a convex shape.
 17. The system of claim 9, whereinthe first reflective surface is a conical surface and wherein an outersurface of the light pipe is conical in shape.
 18. The system of claim17, further including an adhesive material for securing the conicalouter surface of the light pipe to the conical first reflective surfaceof the annular body region.
 19. The system of claim 9, furthercomprising: a light source configured to generate said beam of lightdirected towards said collimating lens; and a light sensor configured toreceive light passing through the bore of the light pipe.
 20. The systemof claim 9, wherein the first reflective surface has a mirror coating.21. The system of claim 9, further comprising a light source configuredto generate said beam of light directed towards said collimating lens.22. A system, comprising: a prismatic light guide comprising: an annularbody region surrounding a conical central opening passing completelythrough the annular body region, the annular body region including afirst reflective surface defined by the conical central opening andfurther including a ring-shaped light output surface surrounding theconical central opening; wherein said first reflective surface isconfigured to internally reflect light propagating within the prismaticlight guide towards said ring-shaped light output surface; and whereinsaid prismatic light guide includes a light input surface configured toreceive a beam of light; and a light pipe having a bore, wherein thelight pipe is mounted within the conical central opening of the annularbody region.
 23. The system of claim 22, wherein the ring-shaped lightoutput surface includes a plurality of microlenses.
 24. The system ofclaim 23, wherein each microlens has a convex shape.
 25. The system ofclaim 22, wherein the first reflective surface has a mirror coating. 26.The system of claim 22, wherein said prismatic light guide furthercomprises a radial projection region extending in a radial directionaway from the annular body region.
 27. The system of claim 22, whereinthe light input surface is defined by a collimating lens.
 28. The systemof claim 26, wherein the radial projection region further includes asecond reflecting surface, wherein said light propagating within theprismatic light guide is reflected by the second reflecting surface in adirection towards the first reflecting surface.
 29. The system of claim28, wherein the light input surface is defined by a collimating lens,and wherein an optical axis of the collimating lens is aligned tointersect with the second reflecting surface.